Electrochemical supercapacitors have gained intense interests in advanced power research field due to its high power density, reversibility, long cycle life and high cycling stability, as well as small environmental impact. Much research carried out on electrochemical capacitors is targeted at increasing power and energy density.
Capacitance of supercapacitors may be divided into two basic types according to their charge storage mechanism. The first basic type relates to electrochemical double layer capacitance (EDLC), which is generated from charge separation at electrode/electrolyte interface, and value of EDLC is determined by the effective surface area and dielectric constant of the electrolyte.
The second basic type relates to pseudocapacitance generated from fast faradic reactions of the electrode material. Materials used to assemble supercapacitor devices are mainly focused on carbon, such as activated carbon, carbon nanotubes, and other porous carbon nanomaterials; metal oxide such as RuO2, MnO2, and IrO2, and conducting polymers such as polyaniline, polypyrrole, and polythiophene.
The energy storage mechanism of all carbon based supercapacitor is EDLC, which has attributes such as long cycle life and good mechanical properties. However, performance of such supercapacitors is dependent on surface area of the material used, which does not involve Faradic reactions. As a result, carbon based supercapacitors have low SC value, which applies also for carbon nanomaterials such as CNT (less than 80 F/g) and chemically reduced graphene oxide (rG-O) (˜150 F/g). Therefore, to increase specific capacitance (SC) value of carbon based capacitors, surface area and pore volume needs to be increased.
Energy storage mechanism of transition metal oxides and CPs are mainly pseudocapacitance, which relies on their reversible faradic reactions accompanied by red/ox and/or doping/dedoping of dopants. Even though pseudocapacitive energy storage mechanism is able to contribute large SC values, rapid degradation due to swelling and shrinkage of the polymers may lead to poor cycle stabilities.
In view of the above, there remains a need for an improved material which may be used in supercapacitor applications and which addresses one or more of the above-mentioned problems.